Epoxy compounds are well known and include many compounds of varying molecular weight and epoxy equivalent weight. To simplify the production of a large number of epoxy compounds that vary mainly in molecular weight, it is common practice to manufacture a single epoxy compound of relatively low molecular weight and react the epoxy compound with a compound containing phenolic hydroxyl groups in the presence of catalyst so as to obtain epoxy of phenolic hydroxy ether compounds of desired higher molecular weight. The conventional catalysts employed are inorganic bases or tertiary amines which are also effective catalysts for competing reactions of epoxides with alcoholic hydroxyl groups, homopolymerization of epoxy groups and the like. As a result, the product obtained is a mixture of polymers and resins with varying degrees of molecular weight, chain branching and end group functionality. Such a composition detracts from the performance and utility of the product. More recent catalysts with improved selectivity include phosphonium halides as disclosed in U.S. Pat. No. 3,477,990, phosphines as disclosed in U.S. Pat. No. 3,547,881, 3-(trihydrocarbylphosphoranylidene)-2,5-pyrrolidinediones as disclosed in U.S. Pat. No. 3,843,605, alkylammonium halides as disclosed in U.S. Pat. No. 3,824,212, and tetrahydrocarbyl phosphonium salts as disclosed in U.S. Pat. No. 4,438,254.
Many of the above catalysts have found commercial utility. However, there is a continuing need for process and product improvements. For example, when many of these catalysts are admixed with the epoxy resins to produce a "pre-catalyzed" epoxy composition, the storage stability at elevated temperatures is not acceptable for many applications because of the reduced activity of the stored resin. U.S. Pat. No. 4,320,222 discloses an improved precatalyzed polyepoxide containing a synergistic catalyst composition comprising a phosphonium halide and an alkali metal halide or hydroxide.
In other cases the process steps must be controlled under strict conditions so as not to deactivate the catalyst. For example, U.S. Pat. No. 4,438,254 cited above requires that the fusion process be conducted at a temperature under 175.degree. C. and under "essentially anhydrous conditions". Patentees define the term "essentially anhydrous" to mean that the reaction medium is absolutely free of water or contains a sufficiently "small quantity of water" not to deactivate the catalyst. The patentees found that deleterious reactions occurred with their catalyst with as little as 0.009 weight percent water present in the reaction medium (column 6, lines 53-58).
What is needed is a new catalyst that does not suffer from deleterious reactions with small quantities of water, thereby enabling much greater freedom of operation. Further, the precatalyzed epoxy resin must be stable at elevated temperature and active at the higher fusion temperatures.